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Overview: Characteristics of Life 1. Living things are highly organized 2. Living things are capable of growing and developing 3. Living things are capable of responding to the environment 4. Living things are capable of reproducing Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell Theory and the Importance of Cells 1. All organisms are made of cells 2. Cells are the basic structural and functional units of life 3. All cells come from other pre-existing cells • The cell is the simplest collection of matter that can live • Cell structure is correlated to cellular function • All cells are related by their descent from earlier cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 6.1 • To study cells, biologists use cell culture, microscopes, and methods in molecular biology and biochemistry (e.g. DNA and protein isolation, cellular localization of proteins, structural determination of proteins, organelle fractionation, etc.) • Though usually too small to be seen by the unaided eye, cells are extraordinarily complex “machines” Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions • The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic • Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells • Protists, fungi, animals, and plants all consist of eukaryotic cells (these are all organisms of the domain Eukarya) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Comparing Prokaryotic and Eukaryotic Cells • Basic features common to all cells: – Plasma membrane – Semifluid substance called the cytosol – Chromosomes (carry genes) – Ribosomes (make proteins) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Prokaryotic cells have no nucleus • In a prokaryotic cell, chromosomal DNA is in an unbound region called the nucleoid; also possess circular pieces of DNA known as plasmids (separate from chromosomal DNA) • Prokaryotic cells lack membrane-bound organelles • Prokaryotic cells possess a cell wall surrounded by a muccopolysaccharide capsule Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-6 Pili Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0.5 µm Flagella A typical rod-shaped bacterium A thin section through the bacterium Bacillus coagulans (TEM) • Eukaryotic cells have DNA in a nucleus that is bounded by a membranous nuclear envelope; have no plasmid DNA • Eukaryotic cells have membrane-bound organelles • Eukaryotic cells are generally much larger than prokaryotic cells (roughly 10X larger) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A Panoramic View of the Eukaryotic Cell • A eukaryotic cell has internal membranes that partition the cell into organelles • Plant and animal cells have most of the same organelles Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-9a ENDOPLASMIC RETICULUM (ER Nuclear envelope Flagellum Rough ER Smooth ER NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes: Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm) LE 6-9b Nuclear envelope NUCLEUS Nucleolus Chromatin Centrosome Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes (small brown dots) Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules CYTOSKELETON Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata Concept 6.3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes • The nucleus contains most of the DNA in a eukaryotic cell • Ribosomes use the information from the DNA to make proteins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Nucleus: Genetic Library of the Cell • The nucleus contains most of the cell’s genes and is usually the most conspicuous organelle • The nuclear envelope encloses the nucleus, separating it from the cytoplasm • Nucleus also contains the suborganelle known as the nucleolus - ribosomal subunits are synthesized here Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-10 Nucleus Nucleus 1 µm Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Pore complex Rough ER Surface of nuclear envelope Ribosome 1 µm 0.25 µm Close-up of nuclear envelope Pore complexes (TEM) Nuclear lamina (TEM) Ribosomes: Protein Factories in the Cell • Ribosomes are particles made of ribosomal RNA and protein • Ribosomes carry out protein synthesis in two locations: – In the cytosol (free ribosomes) - synthesize cytosolic/intracellular proteins – On the outside of the endoplasmic reticulum (ER) or the nuclear envelope (bound ribosomes) - synthesize transmembrane proteins or proteins to be secreted outside of cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-11 Ribosomes ER Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit Small subunit 0.5 µm TEM showing ER and ribosomes Diagram of a ribosome Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell • Components of the endomembrane system: – Nuclear envelope – Endoplasmic reticulum – Golgi apparatus – Lysosomes – Vacuoles – Plasma membrane • These components are either continuous or connected via transfer by vesicles Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Endoplasmic Reticulum: Biosynthetic Factory • The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells • The ER membrane is continuous with the nuclear envelope • There are two distinct regions of ER: – Smooth ER, which lacks ribosomes – Rough ER, with ribosomes studding its surface Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-12 Smooth ER Rough ER Nuclear envelope ER lumen Cisternae Ribosomes Transport vesicle Smooth ER Transitional ER Rough ER 200 nm Functions of Smooth ER • The smooth ER – Synthesizes lipids – Metabolizes carbohydrates – Stores calcium – Detoxifies poison Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Functions of Rough ER • The rough ER – Has bound ribosomes – Produces proteins and membranes, which are distributed by transport vesicles – Is a membrane factory for the cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Golgi Apparatus: Shipping and Receiving Center • The Golgi apparatus consists of flattened membranous sacs called cisternae • Functions of the Golgi apparatus: – Modifies products of the ER – Manufactures certain macromolecules – Sorts and packages materials into transport vesicles Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-13 Golgi apparatus cis face (“receiving” side of Golgi apparatus) Vesicles also transport certain proteins back to ER Vesicles move from ER to Golgi Vesicles coalesce to form new cis Golgi cisternae 0.1 µm Cisternae Cisternal maturation: Golgi cisternae move in a cisto-trans direction Vesicles form and leave Golgi, carrying specific proteins to other locations or to the plasma membrane for secretion Vesicles transport specific proteins backward to newer Golgi cisternae trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus Lysosomes: Digestive Compartments • A lysosome is a membranous sac of hydrolytic enzymes • Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids • Lysosomes also use enzymes to recycle organelles and macromolecules, a process called autophagy Animation: Lysosome Formation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-14a 1 µm Nucleus Lysosome Lysosome contains Food vacuole Hydrolytic active hydrolytic enzymes digest fuses with enzymes food particles lysosome Digestive enzymes Plasma membrane Lysosome Digestion Food vacuole Phagocytosis: lysosome digesting food LE 6-14b Lysosome containing two damaged organelles 1 µm Mitochondrion fragment Peroxisome fragment Lysosome fuses with vesicle containing damaged organelle Hydrolytic enzymes digest organelle components Lysosome Digestion Vesicle containing damaged mitochondrion Autophagy: lysosome breaking down damaged organelle Vacuoles: Diverse Maintenance Compartments • Vesicles and vacuoles (larger versions of vacuoles) are membrane-bound sacs with varied functions • A plant cell or fungal cell may have one or several vacuoles Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Food vacuoles are formed by phagocytosis • Contractile vacuoles, found in many freshwater protists, pump excess water out of cells • Central vacuoles, found in many mature plant cells, hold organic compounds and water Video: Paramecium Vacuole Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-15 Central vacuole Cytosol Tonoplast Nucleus Central vacuole Cell wall Chloroplast 5 µm LE 6-16-1 Nucleus Rough ER Smooth ER Nuclear envelope LE 6-16-2 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle trans Golgi LE 6-16-3 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle Plasma membrane trans Golgi Concept 6.5: Mitochondria and chloroplasts change energy from one form to another • Mitochondria are the sites of cellular respiration • Chloroplasts, found only in plants and algae, are the sites of photosynthesis • Mitochondria and chloroplasts are not part of the endomembrane system • Peroxisomes are oxidative organelles Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mitochondria: Chemical Energy Conversion • Mitochondria are in nearly all eukaryotic cells • They have a smooth outer membrane and an inner membrane folded into cristae • The inner membrane creates two compartments: intermembrane space and mitochondrial matrix • Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix • Cristae present a large surface area for enzymes that synthesize ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-17 Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA 100 nm Chloroplasts: Capture of Light Energy • The chloroplast is a member of a family of organelles called plastids • Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis • Chloroplasts are found in leaves and other green organs of plants and in algae • Chloroplast structure includes: – Thylakoids, membranous sacs – Stroma, the internal fluid Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-18 Chloroplast Ribosomes Stroma Chloroplast DNA Inner and outer membranes Granum 1 µm Thylakoid Peroxisomes: Oxidation • Peroxisomes are specialized metabolic compartments bounded by a single membrane • Peroxisomes breakdown fatty acids or amino acids and some toxins, generating hydrogen peroxide (H2O2) in the process; the H2O2 is then converted to H2O and O2 by the enzyme, catalase Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-19 Chloroplast Peroxisome Mitochondrion 1 µm Concept 6.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cell • The cytoskeleton is a network of fibers extending throughout the cytoplasm • It organizes the cell’s structures and activities, anchoring many organelles • It is composed of three types of molecular structures: – Microtubules – Microfilaments – Intermediate filaments Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-20 Microtubule Microfilaments 0.25 µm Roles of the Cytoskeleton: Support, Motility, and Regulation • The cytoskeleton helps to support the cell and maintain its shape • It interacts with motor proteins to produce motility • Inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton • Recent evidence suggests that the cytoskeleton may help regulate biochemical activities Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 6.7: Extracellular components and connections between cells help coordinate cellular activities • Most cells synthesize and secrete materials that are external to the plasma membrane • These extracellular structures include: – Cell walls of plants – The extracellular matrix (ECM) of animal cells – Intercellular junctions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell Walls of Plants • The cell wall is an extracellular structure that distinguishes plant cells from animal cells • The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water • Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Extracellular Matrix (ECM) of Animal Cells • Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) • The ECM is made up of glycoproteins and other macromolecules • Functions of the ECM: – Support – Adhesion – Movement – Regulation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-29a Collagen fiber EXTRACELLULAR FLUID Fibronectin Plasma membrane Integrin CYTOPLASM Microfilaments Proteoglycan complex Intercellular Junctions • Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact • Intercellular junctions facilitate this contact Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plants: Plasmodesmata • Plasmodesmata are channels that perforate plant cell walls • Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-30 Cell walls Interior of cell Interior of cell 0.5 µm Plasmodesmata Plasma membranes Animals: Tight Junctions, Desmosomes, and Gap Junctions • At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid • Desmosomes (anchoring junctions) fasten cells together into strong sheets • Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells Animation: Tight Junctions Animation: Desmosomes Animation: Gap Junctions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 6-31 Tight junctions prevent fluid from moving across a layer of cells Tight junction 0.5 µm Tight junction Intermediate filaments Desmosome 1 µm Space between cells Gap junctions Plasma membranes of adjacent cells Gap junction Extracellular matrix 0.1 µm The Cell: A Living Unit Greater Than the Sum of Its Parts • Cells rely on the integration of structures and organelles in order to function • For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings